The Streptococcus pyogenes hyaluronic acid capsule promotes experimental nasal and skin infection by preventing neutrophil-mediated clearance

Abstract

Streptococcus pyogenes is a globally prominent human-specific pathogen responsible for an enormous burden of human illnesses, including >600 million pharyngeal and >100 million skin infections each year. Despite intensive efforts that focus on invasive indications, much remains unknown about this bacterium in its natural state during colonization of the nasopharynx and skin. Using acute experimental infection models in HLA-transgenic mice, we evaluated how the hyaluronic acid (HA) capsule contributes to S. pyogenes MGAS8232 infection within these limited biological niches. Herein, we demonstrate that HA capsule expression promotes bacterial burden in murine nasal turbinates and skin lesions by resisting neutrophil-mediated killing. HA capsule production is encoded by the hasABC operon and compared to wildtype S. pyogenes infections, mice infected with a ΔhasA mutant exhibited over a 1000-fold CFU reduction at 48-hours post-nasal challenge, and a 10,000-fold CFU reduction from skin lesions 72-hours post-skin challenge. HA capsule expression contributed substantially to skin lesion size development following subdermal inoculations. In the absence of capsule expression, S. pyogenes revealed drastically impeded growth in whole human blood and increased susceptibility to killing by isolated neutrophils ex vivo, highlighting its important role in resisting phagocytosis. Furthermore, we establish that neutrophil depletion in mice recovered the reduced burden by the ΔhasA mutant in both the nasopharynx and skin. Together, this work confirms that the HA capsule is a key virulence determinant during acute infections by S. pyogenes and demonstrates that its predominant function is to protect S. pyogenes against neutrophil-mediated killing.

Streptolysin S is required for Streptococcus pyogenes nasopharyngeal and skin infection in HLA-transgenic mice

“…Control mice received rat IgG2a clone 2A3 (Cedarlane). Depletion of circulating neutrophils using this protocol has been confirmed in a previous study by flow cytometry of Ly6G + expressing populations in blood and the nasopharynx [32]. Bacterial burden in nasal turbinates was examined at both 48 hours following infection.…”

“…Recently, we have shown that neutrophils are present during experimental nasopharyngeal infection of B6 HLA mice, and that capsule-deficient S . pyogenes exhibits an increased susceptibility to neutrophil-mediated killing [ 32 ]. Thus, we decided to explore whether S .…”

“…In both a zebrafish model of myositis and a murine model of invasive skin infection, SLS-deficient S. pyogenes exhibited increased neutrophil influx to the site of infection [24,31]. Recently, we have shown that neutrophils are present during experimental nasopharyngeal infection of B6 HLA mice, and that capsule-deficient S. pyogenes exhibits an increased susceptibility to neutrophil-mediated killing [32]. Thus, we decided to explore whether S. pyogenes Δsag exhibits a reduction in nasopharyngeal infection due to an increased susceptibility to neutrophil-mediated killing.…”

“…Thus, we decided to explore whether S. pyogenes Δsag exhibits a reduction in nasopharyngeal infection due to an increased susceptibility to neutrophil-mediated killing. Using a previously established protocol [32], mice were rendered neutropenic by administration of 250 μg of an αLy6G antibody, or an isotype control antibody, 24 hours prior to either nasopharyngeal or skin infection, and then given another dose of antibody 24 hours post-infection to ensure neutrophils remained depleted after infection (Fig 4A). Following nasopharyngeal infection, we found that SLS-deficient S. pyogenes was unable to infect neutrophil-depleted mice at comparable levels to the wildtype bacteria (Fig 4B).…”

Outbreak of invasive Group A streptococcus disease in a nursing home in Ireland in February 2023 caused by emm type 18

“…Multilocus sequence typing and SNP-based analysis, though limited, confirmed the relatedness of the three isolates. Further analysis of the three genomes revealed that all three isolates possessed the hasABC operon encoding for the hyaluronic acid capsule and considered to be an important virulence factor of emm 18 strains [ 29 , 34 ]. As reported elsewhere for emm 18 isolates, the three outbreak isolates also harboured the speA gene encoding the SpeA superantigen [ 29 ].…”